The present application relates to communication methods, communication devices and communication systems employing multi-carrier transmission with a power saving mode. In some embodiments, the application relates to corresponding methods, devices and systems also employing retransmission.
Multi-carrier transmission is nowadays employed widely in communication methods, systems and devices. In multi-carrier transmission, data is modulated onto a plurality of carriers having different frequencies, the carriers also being referred to as tones. One example for multi-carrier transmission is discrete multitone modulation (DMT) which is widely employed in DSL (Digital Subscriber Line) communication like ADSL and VDSL communication. Various versions of ADSL and VDSL, like VDSL, VDSL2, ADSL or ADSL2 are standardized by various ITU-T recommendations like G.991.x (x currently being 1 or 2) for HDSL, G.992.x (x currently ranging from 1 to 5) for various ADSL variants or G.993.x (x currently being 1 or 2) for VDSL. Other standards provide addition to such DSL transmission. For example, G.994.1 provides handshake procedures, and G.998.4 provides implementations for improved impulse noise protection including for example retransmission mechanisms where data which is not received correctly is sent again, i.e. is retransmitted. As the details of such systems are standardized, they will not be described again here in detail.
When transmitting data via multi-carrier transmission, each carrier is provided with a certain transmit power. Additionally, for example in some of the above-mentioned DSL standards low power modes have been defined which for example are able to reduce the overall transmit power when no data is to be transmitted. However, these conventional low power modes in some instances may be difficult to employ, for example if a DSL transmission is used for voice over IP (VoIP), i.e. for telephony applications, where some activity may always be required to ensure that a user is always reachable via telephone. Furthermore, in some cases the power saving obtained by such conventional low power modes may not be satisfying.